A traditional tunable antenna element consists of a power splitter, a transformer and a phase adjuster. In high performance antennas, these components are in close association with each other, since these components over-strain strongly interacts with each other, it is sometimes difficult to form a desired beam shape, thus requiring specification phase shifting device to address these problems.
In a first prior art, in the U.S. Pat. No. 5,949,303, a network for adjusting the beam direction of a beam radiated from a stationary array of antenna is disclosed. The beam forming network includes a fixed substrate, a fixed carrying plate accompanied with a feeder line network and movable insulating plate. The insulating plate is placed between the fixed substrate and the fixed carrying plate, so as to achieve phase shifting functions by moving the insulator. The technology has the following disadvantages: first, the insulating plate is overlapped with the plurality of feeder, which increases the loss; second, the insulating plate intersects with multiple locations on the feeder line network, which increases the reflective signal and is disadvantageous for the design of wide-band; third, the arrangement order of the output end conflicts with that of the radiating unit of the linear antenna array, which increases the complexity of connection between the output end and the radiating unit and also increases the length of connecting cable between the output and the radiating element, increasing costs and loss; fourth, this method is not applicable to a linear antenna array having odd output ports.
In a second prior art, in a European patent WO 03/019723, an antenna feeding network with an integrated phase shifter is disclosed. The device includes a branch network of common feeder line with multiple ports, and a dielectric plate mounted adjacent to the network. The dielectric plate is movable so as to synchronously adjust the phase relationship between the common feeder line and one or more ports. The technology has the following disadvantages: first, the device employs a monolith elongated dielectric plate which is prone to deform, thus affecting the stability of the overall device performance; second, the elongated dielectric plate is in contact with feeder line in a bigger area, a large friction is generated between the dielectric plate and the feeder line during moving, which causes the feeder circuit to be worn, resulting in an unstable third order intermodulation of the device; third, the dielectric plate intersects with multiple feeder lines, which increases the reflected signals and is disadvantageous for the design of wide-band; Fourth, the dielectric plate is overlapped with the multiple feeder line, which increases the loss.
FIG. 1 is a drawing of a ten-ports device of an embodiment provided by the second prior art, wherein a stripline 18 is located between an insulator 47a and an insulator 47b. When the insulator 47a and the insulator 47b synchronously moves towards the same direction, the differences between the individual adjacent ports are synchronously changed, and the biggest phase difference is determined by the distance of moving of the insulator 47a, 47b, that is determined by the length of the stripline 18. The phase difference between the adjacent output ports is in proportion to the downtilt angle of the antenna array. The stripline 18 is of a straight line shape and is applicable to an antenna array with a small downtilt angle (for example a downtilt angle of 10 degree). If the device is used in an antenna array with a large downtilt angle (for example greater than a downtilt angle of 15 degree), it needs to increase significantly the length of the stripline 18, so that the overall length of the device is far greater than the length of the antenna array, increasing the length, the cost and the complexity of the antenna. Correspondingly, the length of the insulator 47a, 47b needs to be greatly increased. Since the insulator 47a, 47b generally is formed of plastic, if the length is too long, the insulator 47a, 47b easily deformed, which affects the stability of the overall performance of the device. Additionally, the insulator 47a, 47b greatly covers the stripline 18 and the power divider, increasing the loss of the device.
In view of above, the phase-shifting device in prior art has limited application, and is not applicable in the antenna array with a large downtilt. The area of the insulator in the device is relative large, which increases the manufacturing accuracy, difficulty and cost of the insulator, and the insulator is easily deformed, the insulator overlaps with the most of the feeder line, increasing the loss.